Energy Value of Feed Ingredients for Pigs

[NOTE: Download Table 3 and Table 4 Here.]

INTRODUCTION

Feed represents the greatest single expense associated with rearing pigs to slaughter. Therefore it is possible to improve the economics of pig production if this cost can be reduced without affecting pig performance. However, in recent times, the majority of diets fed to pigs are based on wheat, barley and soya bean meal. Pigs are opportunity feeders and have the ability to consume all manner of feedstuffs. There are many sources of dietary energy and protein that have the potential for use in pig production. Most of these raw materials are by-products of different industries and are therefore available in large quantities at low cost. However, the successful incorporation of many of these ingredients can be limited by availability of sufficient information on which to base ration formulation and feeding recommendations.

IN DIVO DIGESTIBILITY EXPERIMENT IN UCD

This bulletin contains information relating to 25 feed ingredients fed to pigs in Ireland. A brief description of the feed and its origin is given along with composition and digestibility of samples tested under standard conditions in UCD. A comment is given on the feed's value for pigs. These feeds included cereals, cereal by-products, citrus and sugarbeet pulps and vegetable proteins and legumes. 

Twenty-five ingredients were tested in a 4 x 4 Latin Square designed digestibility experiment. Each Latin Square contained 3 test ingredients and a basal diet. The pigs weighed 40 kg at the beginning of the experiment and were 90 kg at the end and on average weighed 65 kg. The pigs were housed in metabolism cages fitted with urine and faeces separators. The cages were located in an environmentally controlled room, maintained at a constant temperature of 20 0 C. The study consisted of an initial 10 days acclimatisation period and a further 10 days during which feed intake and faeces output were recorded. Food was presented to each animal twice daily in the form of meal mixed with water in the proportion 1:2 w/v and restricted according to a scale of 90% ad-libitum intake. The ad-libitum feed intake was measured during the acclimatisation period. The test ingredients were sourced from the main grain and feed importers in Ireland while the cereals and beans were sourced from local tillage farmers. The non-cereal feed ingredients examined, their inclusion levels in the test diet, experimental codes and country of origin are presented in Table 1. 

 The cereals examined, their hectolitre weight and inclusion level are presented in Table 2.  

The chemical composition and digestibility coefficients of all by-products, protein sources and cereals examined in the present study are presented in Table 3 and Table 4. The predicted Net Energy (NEg) of the ingredients was calculated from the following equation (Noblet, Fortune, Shi and Dubois, 1994):

NEg = 0.703 (DE) - 0.041 (CP) + 0.0066 (ether extract) - 0.0041 (CF) + 0.0020 (starch)
(NEg in MJ/kg DM, composition in g/kg DM)

Sugar beet pulp
Dried sugar beet pulp is the residue remaining after extraction of sugar from sugarbeet. The average digestible energy content (DE) of the unmolassed sugar beet pulp obtained in the present study was 11.1 MJ/kg. This value is higher than the international average value of 10.3 MJ/kg quoted by others (R&H Hall, 1996; NRC, 1998). However, there was some variation between the beet pulps used in this study. BP99 had a higher DE content than the BP98 sample (11.6 MJ/kg vs. 10.6 MJ/kg)(see Table 3). The neutral detergent fibre (NDF) digestibility coefficient was extremely high for both beet pulps. This NDF is in the form of hemicellulose, which is more readily fermented than other fibrous materials and can make a significant contribution to the energy nutrition of the pig provided the quantity of beet pulp in the diet is not too great. Unmolassed sugar beet pulp can be used at levels of 10 to 15% in grower finisher pig diets (Longland and Low, 1988) while pregnant sows could be fed 30% sugar beet pulp in a cereal based diet without affecting performance (Mentler, 1966).

Citrus pulp 
Citrus pulp is a by-product of the fresh citrus fruit industry. The chemical composition of the two samples of citrus pulp examined in this study were similar to that of other internationally reported values (NRC, 1998, R&H Hall, 1996). The average DE content of 11.6 MJ/kg compares well with the R&H Hall (1996) value of 12.0 MJ/kg. There was some variation between the 2 batches of citrus pulp used, which may be explained by the better NDF digestibility. As in sugar beet pulp, hemicellulose is a major fibre in citrus pulp, which makes it a useful source of energy in grower-finisher pig diets. Research at Moorepark (O' Sullivan, Lynch and Morrissey, 1994) showed that pig performance was not affected by the inclusion of 5% citrus pulp in the diet, however inclusion of 10% resulted in poorer pig performance.

Copra 
Coconut or copra meal is the residue remaining after removal and drying the meal of the coconut. In our study, the higher oil content of the expeller copra meal resulted in a much higher DE content than for the extractor copra meal (13.6 MJ/kg vs. 11.2 MJ/kg). The DE of expeller copra in the present experiment compares well with the DE value of 14.0 MJ/kg given by R&H Hall (1996). 

Recent experiments at Lyons Research Farm (O' Doherty and McKeon, 2000) showed the inclusion of 20% expeller copra meal does not affect pig performance but may reduce killing out proportion. High levels of copra meal should be very favourable for heavy pigs (> 65 kg) and pregnant sows. 

Maize Distillers 
Maize distillers grains are a by-product of the use of maize by the distilling industry. The average DE content (11.0 MJ/kg) of the maize distillers used in the current study was lower than that reported in other data bases (13.0 MJ/kg, R & H Hall, 1996; NRC, 1998). The NDF content of the sample examined was higher than other data bases (485.5 g/kg vs. 340 g/kg, respectively). There was big variation between the maize distillers in this study. MD98 had a higher DE content than the MD99 sample (11.8 MJ/kg vs. 10.2 MJ/kg) (see Table 3). Maize distillers is a good source of protein, however the protein is of low digestibility.

Maize Gluten 
Maize gluten feed is the part of the commercially shelled maize that remains after extraction of the larger part of the starch, gluten, and germ by the processes used in the wet milling manufacture of maize starch or syrup. 

The chemical composition of each of the samples examined was similar. Because of its fibre content maize gluten has an average DE content. The average DE content of maize gluten (11 MJ/kg) found in the present study compares favourably with the value of 10.6 MJ/kg DE given by R&H Hall (1996). Maize gluten is similar in digestibility to maize distillers. It has an average protein content and low protein digestibility. The poor availability of the lysine and tryptophan in corn gluten feed, along with its high fibre and low DE, limits its usefulness in pig diets. Research at Moorepark (Kavanagh, 1998) showed that pig performance was not affected by the inclusion of 15% maize gluten feed, when included in cereal based diets. 

Malt Sprouts
Malt sprouts are a by-product of malting, consisting of mainly dried rootlets and sprouts usually from germinated barley. The digestibility of malt sprouts was found to be very low. Approximately half of the dry matter and energy content of the examined sample was digested. Digestion of neutral detergent fibre at 0.185 was extremely poor and there was a large coefficient of variation between animals. Malts sprouts have a very low DE content of 8.6 MJ/kg. 

Palm Kernel meal 
Palm kernel meal is the residue after the removal of oil from the nut of the oil palm. The vast majority (>70%) of Palm Kernel meal imported into Ireland is Malaysian / Indonesian in origin rather than African.

In the current study, the digestibility of African palm kernel was low with an energy digestibility of 58%. Despite the high oil content, the high fibre component of palm kernel meal resulted in a relatively low DE content of 10.5 MJ/kg. The high crude fibre content of African palm kernel meal limits its use in pig diets. 

Pollard 
Pollard is a by-product of flour manufacture. The current study found pollard to be an excellent source of energy for pigs with a DE value of 12.6 MJ/kg. R&H Hall previously reported a much lower DE content for pollard of 10.6 MJ/kg. The NRC (1998) report a DE content for pollard of 12.86 MJ/kg, which is much closer to the value obtained in the present study. The favourable protein digestibility of pollard along with its average energy content make it a very useful feedstuff for grower-finisher pig diets. Recent experiments at Lyons Research Farm have shown that 15 to 20% Irish pollard can be used in finisher pig diets without affecting pig performance. 

Soya Hulls 
Soya hulls is a by-product of the soya bean oil industry. There was some variation between the soya hulls in this study. SH98 had a higher DE than the SH99 sample (9.9 MJ/kg vs. 8.3 MJ/kg)(see Table 3). The neutral detergent fibre (NDF) digestibility coefficient was lower in the latter sample. Soya hulls is a poor energy source for pig diets. It contains 10 per cent protein only half of which is actually digestible.

Sunflower meal 
Sunflower meal is the residue remaining after the removal of oil from sunflower seeds. The extent of decortication is variable which has a big effect on feeding value as the hulls are very indigestible. Sunflower meal in the current study had a low DE content of 8.6 MJ/kg, which compares well with the NRC (1998) value of 8.4 MJ/kg. Sunflower meal has a high crude protein content (289 g/kg), which is of poor digestibility. As an energy source, sunflower meal is poor and very variable. 

[NOTE: Download Table 3 and Table 4 Here.]

PROTEIN SOURCES

Peas 
Peas are a good protein and energy source for pig diets. In the current study, the high digestibility of peas resulted in a DE content of 14 MJ/kg. Peas are a good source of protein for pigs, being high in lysine but however, deficient in the sulphur containing amino acids. This deficiency in sulphur containing amino acids could lead to a decrease in animal performance if not corrected. Peas contain several natural constituents, which can interfere with their utilisation or disrupt the physiological processes of the pig. The major concerns for pigs are the presence of protease inhibitors, lectins, tannins and a-galactosides. Recent research from Lyons Research Farm (O' Doherty and Keady, 2000) found that peas can be used safely in growing finishing diets up to 200 g/kg. Heat treated field peas, though can be incorporated at much higher levels up to 400 g/kg.

Soya Bean meal
Whole soya beans contain 15-21% oil, which is removed by solvent extraction or by a combination of mechanical procedures and solvent extraction. In processing, the meal is toasted, a procedure that improves the biological value of its protein by destroying various inhibitors. Soya bean meal is a highly favoured feed ingredient because of its palatability, digestibility and high energy value.

The average DE of the soya bean meal obtained in the present study was 15 MJ/kg. Soya bean meal has a very high protein and energy digestibility. There was a small difference in DE content between the samples examined, which highlights the variation in energy content between different batches. 

Rapeseed meal
Rape seed meal is the by-product remaining after removal of oil from rape seed. The average DE content of 11.8 MJ/kg found in the present study is lower than the R&H Hall (1996) value of 12.3 MJ/kg. The presence of anti-nutritional glucosinolates, limits the use of rapeseed meal in pig diets. Recent experiments at Lyons Research Farm (Keady and O' Doherty, 2000) found that there was a linear decrease in growth rate and a linear deterioration in FCR as the level of rapeseed meal increased in the diet. Rapeseed meal can be used at levels of 12.5% in grower finisher pig diets without affecting pig performance.

EFFECT OF INCLUSION LEVEL

It should be noted that the 40% inclusion level for all ingredients may discriminate against ingredients that, in practice, would not be included at that level due to anti-nutritional factors and high fibre levels and in practice their energy value could be higher. Recent work at Lyons Research Farm showed that the inclusion of 40% peas in the diet led to a lower DE content (0.75 MJ/kg) of the peas compared to 20% peas (O' Doherty and Keady, 2000). Similar observations were reported for rapeseed meal (0.5 MJ/kg decrease) and copra meal (0.7 MJ/kg decrease) when included at 20% and 40% in the diet.

CEREALS

Hectolitre weight or 'bushel weight' is the standard measure of cereal quality in Ireland. In this study we looked at the relationship between DE content and hectolitre weight of wheat and barley.

Barley
The low hectolitre weight barley (58.5 kg/hl) had the lowest DE content of the 3 different hectolitre weights. There was no real difference in DE content between the high (68.5 kg/hl) and medium (60.8 kg/hl) hectolitre weight barley. The average DE content (12.8 MJ/kg) of the three barleys in the present study is lower than other quoted values of 13.6 MJ/kg (NRC, 1998, R&H Hall, 1996, CVB, 1991, MAFF, 1990). Low hectolitre weight barley had the highest fibre content and as a result the lowest DE content. The differences in chemical composition between the medium and high hectolitre weight barley samples were not great enough to cause a difference in DE content.

Wheat
There was no real difference in DE content between the high and medium hectolitre weight wheats. The low hectolitre weight wheat had a DE content of 12.2 MJ/kg while the medium and high hectolitre wheats had a DE content of 13.1 MJ/kg. The average DE content of the medium and high hectolitre weight wheats examined in the present study (13.1 MJ/kg) does not compare favourably with the average internationally reported value (NRC, 1998, R&H Hall, 1996, CVB, 1991, MAFF, 1990). Hectolitre weight has been shown to be an unreliable predictor of flour yield (Schuler et al. 1995) due to its inability to distinguish between low-density kernels resulting from shrivelled, poorly filled, or damaged grain from well-filled grain. However, a significant decrease in DE content was found in low hectolitre weights of barley and wheat. Therefore, hectolitre weight should only be used when comparing cereals of high and low quality. It cannot be reliably used to compare cereals of high and medium quality. Interestingly, when all the wheats were expressed on a Dry Matter basis there was no difference in the DE content between them. 

CONCLUSION

There was a considerable amount of variation in DE content between different sources and different batches of ingredients. This highlights the necessity for the development of accurate and rapid methods of feed analysis such as NIRS (Near Infrared Spectrophotometry) to enable the measurement of quality control of imported feeds. 

MAIN REFERENCES

Centraal Veevoederbureau, (1991). Veevoedertabel, CVB, Runderweg 6, Leylystad, The Netherlands.
Kavanagh, S., (1998). Studies on the nutritive value of feedstuffs for pigs. Ph.D thesis. National University of Ireland.
Keady, U. and O'Doherty, J.V. (2000). The effect of extrusion on the nutritive value of rape seed meal for growing and finishing pigs. Irish Journal of Agriculture and Food Research 39, 3, 419-431.
Longland, A.C., Low, A.G., Keal, H.D. and Harland, J.I. (1988). Dried molassed and plain sugarbeet in diets for growing pigs. Proceedings of Nutrition Society 47: 102A
McKeon, M.P. and O'Doherty, J.V. (2001). A note on the nutritive value of extruded and raw beans for growing and finishing pigs. Irish Journal of Agriculture and Food Research (In Press).
Mentler, L. (1966). Unprocessed sugarbeet pulp for breeding sows. Allattenyesztes 15: 43-44
National Research Council, (1998). Nutrient Requirements of Swine. 10th Revised edition, Washington D.C: National Academy Press.
O'Doherty, J.V. and Keady, U. (2000) The effect of extrusion on the nutritive value of peas for growing and finishing pigs. Animal Science 70: 265-274
O'Doherty, J.V. and McKeon, M.P. (2000). The use of expeller copra meal in grower and finisher pig diets. Livestock Production Science 67: 55-65.
R and H Hall Feed Tables (1996). Technical Bulletin. Issue No. 5 - 1996.

ABOUT THE AUTHORS

Dr. John O'Doherty is a lecturer in Pig Husbandry in the Faculty of Agriculture at UCD.
Mr. Michael Dore completed a Masters Degree in pig nutrition at UCD.